Method of centrifugally casting pipes in chilled molds



Patented Sept. 6, 1938 METHOD OF CENTRIFUGALLY CASTING PIPES IN CHILLEDMOLDS Eugen Piwowarsky, Aachen, Germany No Drawing. Application June 23,193G, Serial No. 86,751. In Germany July 1, 1935 2 Claims. (Cl. 148-3)The present practice in producing cast-iron pipes centrifugally,preferably in cooled molds,

is the use oi cast-iron which contains ordinarily over 3% of carbon witha corresponding propor- 5 tion of silicon. Such centrifuged pipes, whichmay if necessary be annealed after the centrifuging operation, have goodstrength combined with high resistance to corrosion.

In order to produce centrifugally-cast pipes which have extremely highstrength and an unusually high resistance to shock, according to thepresent invention it is proposed to use a cast iron of which not onlythe carbon content but also the total content of carbon and silicon to-0 l5 gether is maintained low. Thus very good results have been obtainedby using cast-iron containing less than 2.4% of carbon and in which thesum of C+Si varies between 3 and 4%. Experiments have shown that byusing this cast-iron according to the invention, itis possible to obtaincentrifugally cast pipes which have after the known annealing operationgood resistance to corrosion and high coefficient of resistance to shockof over 3 mkg.

Furthermore it has been found that the tensile strength, and moreparticularly the resistance to shock, can be still increased in thepipes produced from the cast-iron according to the invention bysubjecting them after the known annealing operation to an additionalimproving heat treatment carried out at temperatures lying between 200and 600 0., preferably between 250 and 350 C.

This improving heat treatment may either be efiected on the pipesalready cooled after the annealing operation. It may also be carried outafter the completion of the known annealing operation, by firstquenching the pipes by air, oil or water, from temperatures of about 20to 80. C. above the conversion point A 1, 2, a, whereupon the improvingheat treatment according to the invention follows. Centrifugallycast-pipes subjected to this improving heat treatment possess not onlyhigh strength but also high coefficient of resistance to shock of over 4mkg.

The invention is not confined to the application of this improving heattreatment to centrifugally cast pipes made from cast-iron according tothe invention containing less than 2.4% of carbon, and having a contentof C+Si of from 3 to 4%, but extends also to the application of theimproving heat treatment to centrifugally cast pipes made of cast-ironin which the carbon content is a little higher, but is under 3%, and thecontent of C+Si is likewise a little higher, that is to say, up to about5.5%, as an appreciable increase in the resistance to shock ofcentrifugally-cast pipes in the production of which such cast-iron isused, is produced by the improving heat treatment according to theinvention.

Furthermore, when using an alloyed castiron to which are added alloyingconstituents producing white iron, the carbon content and the sum of thecontents C+Si may be correspondingly higher than first indicated, whensubjected to the improving heat treatment.

What I claim 1S1 to impact shocks is produced.

2. The method claimed in claim 1, in which said pipe is reheated, afterthe annealing step, at temperatures ranging between 200 and 600 6.,whereby the shock resistance of said pipe is further increased.

EU GEN PIWOWARSKY.

